Researchers monitored the intellectual capacity of more than 600 vineyard workers for up to six years.
They found those who had been directly exposed to pesticides were more likely to perform worse in cognitive tests at the end of the study period than they had at the start.

Workers exposed to pesticides were twice as likely to drop two points in the mental state exam, one of nine tests, as those who had not been exposed.

The authors of the study said this was "particularly striking in view of the short duration of follow-up and young age of participants".

They said: "The mild impairment we observed raises the question of higher risks of injury in this population and also of the possible evolution towards neurodegenerative diseases such as Alzheimer's."